Catheters are well known in medicine and a wide variety exist for a variety of purposes. Catheters are typically flexible tubes of varying sizes that are inserted into the body. One common application of catheters, for example, is the removal of bodily fluids from the bladder during the time when the patient is incapacitated. As the technology of medicine has expanded, catheters are becoming more widely used for a greater variety of purposes.
Catheters exist that have pressure sensors at the distal tip. When these pressure sensors are inserted into the body, the local pressure around the distal tip of the catheter is able to be measured. In general, these prior art pressure sensors are usually used to measure the pressure of solid body parts against the catheter, and not air pressure in spaces filled with air.
Catheters also exist that have on their distal end a pH sensor. In these types of catheters, an electrical wire runs inside the catheter to the proximal end of the catheter. When the catheter is inserted into the body, this arrangement permits the electrical sensing of pH (that is, acidity) of the immediate environment of the distal tip. Such pH catheters are presently manufactured by Synectics Medical AB of Sweden, distributed in the U.S. by Synectics Medical, Inc. of 1425 Greenway Drive, Suite 600, Irving, Tex.
A lumen is a channel inside the catheter that runs the length of the catheter. Multiple lumen catheters are well known. These catheters can function much like multiple catheters with each lumen dedicated to one function. As such, a single catheter with multiple lumens can operate as a multiple function catheter. Since the diameter of the catheter is of critical importance, it becomes difficult to incorporate a large number of lumens within a single catheter. The restriction of space availability inhibits the ability to incorporate many functions into one catheter.
Several methods are known that attempt to measure the degree of effort a patient is exerting in the attempt to breathe. The degree of effort exerted in the attempt to breathe is identified as "respiratory effort". Such methods include applying stretch sensitive belts (similar to strain gauges) to the outside of the abdomen, or the application of electrodes to the chest to measure changes in impedance. These approaches are cumbersome and inaccurate. The most accurate technique for measuring respiratory effort is through measuring air pressure changes in the esophagus or stomach. An effort to inhale results in an air pressure drop in the esophagus and trachea, and in a pressure increase in the stomach. This happens even though real inspiration and movement of air from the ambient room to the patient's lungs may not necessarily follow due to, for example, pharyngeal obstruction. An effort to exhale causes analogue events, but in the opposite directions (that is, an air pressure increase in the esophagus and trachea, and a drop in the stomach). When no effort to breathe occurs, the air pressure is these areas will remain constant.
The prior art in the area of respiratory effort in the esophagus includes placing a balloon made from the finger of a latex glove on the end of an esophageal catheter. The balloon is then partially inflated. An air pressure monitor at the proximal end of the catheter connected to the balloon indicates respiratory effort. The relatively large size of the balloon often interfered with the esophageal function and other simultaneous intraesophageal catheterizations. Prior art includes using a small balloon fixed to a piece of tubing and connected to an exterior pressure transducer as in U.S. Pat. No. 4,981,470, issued on Jan. 1, 1991 to Bombeck. This design still has the disadvantage that it is relatively large, expensive and difficult to produce. Also this design can only be used to monitor respiratory effort and not actual respiration.
Prior art to monitor respiratory effort also includes the use of a somewhat inflated balloon communicating with a pressure transducer via plastic tubing. The balloon is taped externally onto the stomach so that inspirations and expirations stretch the balloon thereby creating positive and negative pressure fluctuations in the tubing. The tubing communicates with the pressure transducer monitoring respiratory effort, rather than air flow. This method does not measure pressure changes due to movement of air in, or in the proximity of, the lung airways or the esophagus. This method is also less sensitive and more prone to errors due to body movement or badly taped sensors.
Prior art to measure respiration, that is actual movements of air in and out of the respiratory organs such as the nostrils, uses thermistors that monitor the temperature of respiratory air. This is based on the idea that inspiratory air is cooler than expiratory air. Such thermistors are not connected to pressure transducers. Alternatively pneumotachographs exist where two pressure sensors in series monitor pressure drops over a resistor. This is used to calculate air flow and volume, which information is used in turn to calculate peak flow and tidal volumes. This method is however complicated and expensive and introduces "dead space" as it extends the breathing circuit.
Soviet Patent No. 272,477, issued on May 20, 1968 to Leya and Berzinsh, teaches a stomach-intestinal probe consisting of multiple antimony electrodes to measure stomach acids and a large inflatable balloon to fix the probe in the esophagus so that fluoroscopy can be used to watch the movement of the stomach. This probe permits simultaneous monitoring of stomach acid and stomach movements. However, the balloon is relatively large and blocks esophagus function, thus breaking normal sleep patterns. Also, the balloon cannot function as a pressure sensor since it is too large and not connected to an external pressure monitor.
German Patent No. 2,162,656, issued to Wolters and Eckert on Jun. 20, 1973, teaches a stomach acid gauge with an electrical pH sensor. Once again, this device does not measure respiratory effort. Similar one-function stomach acid sensors are taught by U.S. Pat. No. 4,618,929, issued on Oct. 21, 1986 to Miller et al. al. and by U.S. Pat. No. 4,176,659 issued on Dec. 4, 1979 to Rolfe.
U.S. Pat. No. 4,503,859, issued on Mar. 12, 1985, to Petty, et al., teaches a device to simultaneously monitor esophageal acid and heart EKG. This device does not measure respiratory effort in any way.
German Patent No. DE 3523987A, issued on Jan. 8, 1987, to Lange, teaches a method to measure stomach function consisting of multiple pH sensors attached to the outside of a balloon on a catheter. The balloon, however, is used only to inflate inside the stomach and thereby distribute the pH sensors against the stomach wall. Normal esophageal function is blocked, pH in the esophagus is not tested, and respiratory effort is not measured.
U.S. Pat. No. 4,681,116, issued on Jul. 21, 1987, to Settler, teaches an antimony electrode used as an esophageal electrode. This uses an epoxy resin as a sealant. This is also a single function device which does not simultaneously monitor respiratory effort.
Sleep apnea is the problem of inadequate breathing while asleep. It can have several causes, with each cause requiring different remedies. Hence, individual treatment of sleep apnea can follow only after study of the causes of sleep apnea in the individual.
One alternative cause of sleep apnea is gastroesophageal reflux (GER). GER is the process by which the subject generates acids in the stomach, which are then passed into the esophagus. These acids can then be aspirated into the lungs, causing a constriction of the trachea and difficulty in breathing. However, GER can also be a result instead of a cause, of sleep apnea. Difficulty in breathing, caused by other reasons, can lead to increased respiratory effort in compensation. This increased effort can then encourage GER. In effect, this causes a sucking of the gastric acid into the esophagus from the stomach.
Yet other causes of apneas in the sleep apnea syndrome may be of neurological origin or, more often, from obstruction due to the collapse of the posterior pharyngeal wall during inspiration. Such obstruction may be partial and give rise to the snoring sound. In obstruction sleep apnea the patient's respiratory efforts may not result in adequate movement of air into and out of the patient's lungs in spite of adequate respiratory efforts.
Therefore, to determine the cause of an individual's cause of sleep apnea, and to determine the proper remedy, it is necessary in each individual case to study and sort out the cause and effect relationship of GER, respiratory effort, and respiration (movement of air in the upper airways). In practice, this requires the accurate simultaneous measurement of intraesophageal acid, respiratory effort, and respiration. Specifically, this means the accurate simultaneous measurement of pH in the esophagus, air pressure in the esophagus, and air pressure or air flow in the proximity of the mouth and nostrils. It is also important that this should be done in a way that does not disturb normal sleep, and other bed activity. Unfortunately, no techniques have been developed prior to the present invention which measure all of these factors simultaneously. As a result, the effective study and remedy of sleep apnea is not yet available to medical specialists.
It is an object of this invention to provide a catheter that monitors respiratory effort in the upper gastrointestinal tract (the stomach and esophagus) distal to any nasal or pharyngeal obstructions without using a balloon.
It is another object of this invention to provide a catheter that monitors respiration using the same design as for respiratory effort only placing the monitoring site (that is, the inlet to the catheter) proximal to a possible obstruction site.
It is yet another object of this invention to provide a catheter that monitors both respiratory effort and respiration by using tubing with more than one lumen and the technology described above.
It is yet another object of this invention to provide a catheter that can localize nasal or pharyngeal obstructions using one or more lumens in the tubing, or one or more catheters and the technology described above.
It is yet another object of this invention to provide a catheter that is designed according to any of the objects described above and that includes one or more pH measuring points.
It is an object of the present invention to provide a catheter that monitors movements of air by means of a single air pressure transducer inside or in the immediate proximity of the upper airways such as the nostrils (to measure respiration) or in the esophagus (to measure respiratory effort) or both, without the introduction of dead space and with or without a pH sensor included.
It is another object of the present invention to provide such a catheter that can be utilized without disturbing sleep.
It is a further object of the present invention to provide such a catheter that is compatible with fluoroscopy techniques.
It is still a further object of the present invention to provide an instrument that simultaneously monitors gastric reflux, respiratory effort, and respiration.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.